 | This article may be too technical for most readers to understand. (December 2020) |
The ISO metric screw thread is the most commonly used type of general-purpose screw thread worldwide.[1] They were one of the first international standards agreed when the International Organization for Standardization (ISO) was set up in 1947.[citation needed]
The "M" designation for metric screws indicates the nominal outer diameter of the screw thread, in millimetres. This is also referred to as the "major" diameter in the information below. It indicates the diameter of smooth-walled hole that a male thread (e.g. on a bolt) will pass through easily to connect to an internally threaded component (e.g. a nut) on the other side. For example, an M6 screw has a nominal outer diameter of 6 millimetres and will therefore be a well-located, co-axial fit in a hole drilled to 6 mm diameter.
- ^ ISO/TC/ 1 Business Plan, 2007-03-05, Version 1.3. Table 3: The market share of each screw thread, p. 7.